Snap On has a nice downloadable catalog, similar to Starrett's. Whether you buy Snap On tools or not, I highly recommend downloading it.
It includes detailed specifications of their tools, providing tool buyers with a way to easily compare what they are buying against Snap On's product line. How long is a long pattern wrench? How shallow is a shallow socket?
It includes application data e.g. what specific cars, and applications a specialty tool is designed for. Can be a good idea to search your vehicle to see what specialty tools are out there or what you might need. I didn't know some Mercedes and BMW had 14mm spark plugs. I only have 5/8" and 13/16" plug sockets from Sears.
Last, the tool sizes included in the sets are chosen based on what sizes auto mechanics need most. You can use the sizes included in Snap On's sets as a guide for what you are liable to encounter. Examples include "specialty" tools (what size Secure torx will I need? What about triple squares?). But you can also get a sense for basic tools. Do I need a 26mm impact socket? Snap On makes one, but doesn't include it in their sets, which tells you something. They don't make a 28mm or a 31mm, 33, 35, 37 impact sockets.
